<html>
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var value1="123";
        var value2=0;
        var value3=null;
        var value4;
        var value5=true;
        var value6="a"-1;
        console.log(typeof(value1));//string 字符串
        console.log(typeof(value2));//number 数值
        console.log(typeof(value3));//obiect 对象或null
        console.log(typeof(value4));//undefined 未定义
        console.log(typeof(value5));//buulean 布尔值
        console.log(typeof(value6));//number 数值
    </script>
</body>
</html>